ED usually has an underlying physical cause, such as hypertension, diabetes mellitus, hypercholesterolaemia or cardiovascular disease. These need to be considered when treating ED but are not necessarily reasons to withhold sildenafil, except in certain circumstances.

A number of prescribed drugs are also associated with ED (see Table 1 below). If it is suspected that these drugs are causing, or have aggravated ED, the patient may need to see a doctor, as stopping the medication or an alternative treatment may be appropriate.

Psychological causes account for one in 10 cases of ED. Psychological causes can include: